A crossover with Chicago Fire (Season 5, Ep. 9) where Kelly Severide is suspected of vehicular manslaughter.
In "All Cylinders Firing," Desk Sergeant Trudy Platt (Amy Morton) is brutally attacked outside her father's home, leading to a personal and harrowing investigation into her past.
's fourth season is a pivotal chapter that fundamentally altered the series' trajectory through major cast departures and a shift toward more topical story arcs. Airing from September 2016 to May 2017, the season consists of 23 episodes focused on the professional and personal fallout of Sgt. Hank Voight's (Jason Beghe) vigilante actions. 🎬 Key Character Departures and Arrivals
The season begins with Commander Emma Crowley (Barbara Eve Harris) investigating Voight and Lindsay for the murder of Justin Voight’s killer, a dark secret that strains their relationship.
In a devastating multi-episode arc, Alvin Olinsky (Elias Koteas) loses his daughter, Lexi, in a warehouse fire, pushing him to a grief-stricken breaking point.
Season 4 featured several "One Chicago" crossovers that connected the unit to Chicago Fire and Chicago Med :
Season 4 marked the end of an era for two of the show's original leads and introduced a future mainstay:
